Process for the production of straight-bead welded pipe

ABSTRACT

Straight-bead welded pipe with an entirely homogeneous gain structure is produced by plastic deformation of the welded pipe, specifically in the area of the weld seam, to substantially destroy the weld-induced variations in grain structure and provide nuclei for new, equiaxed grains. A grain texture is avoided by effecting deformation in two directions with two distinct stresses: bending the pipe away from and back to its axis deforms it in the transverse plane, and compressing the pipe along the weld bead deforms it in the longitudinal plane. Thereafter, the pipe is straightened, annealed and, if desired, reduced to finished diameter and wall thickness.

United States Patent n91 Ziemek 451 Apr. 24, 1973 [75] Inventor: GerhardZiemek, Hanover, Ger

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[73] Assignee: Kabel-und Metallwerke Gutehoffnungshutte, Hanover,Germany [22] Filed: Oct. 4, 1971 [21] Appl. No.: 186,173

[30] Foreign Application Priority Data [56] References Cited UNITEDSTATES PATENTS Schmidt et al... ..'..72/364 Allen et al.

3,535,484 10/1970 Snow et al. ..l48/l27 X 3,590,622 7/1971 Elge et a]....29/477.7 X 3,648,353 3/1972 Anderson ...29/487 X 3,663,311 5/1972Chen et al. ..l48/l 1.5

Primary Examiner-J. Spencer Overholser Assistant ExaminerRichard BernardLazarus Att0rneyMarn and Jangarathis [5 7 ABSTRACT Straight-bead weldedpipe with an entirely homogeneous gain structure is produced by plasticdeformation of the welded pipe, specifically in the area of the weldseam, to substantially destroy the weld-induced variations in grainstructure and provide nuclei for new, equiaxed grains. A grain textureis avoided by effecting deformation in two directions with two distinctstresses: bending the pipe away from and back to its axis deforms it inthe transverse plane, and compressing the pipe along the weld beaddeforms it in the longitudinal plane. Thereafter, the pipe isstraightened, annealed and, if desired, reduced to finished diameter andwall thickness.

7 Claims, 4 Drawing Figures Patented April 24 1973 VFIG.|

m/vg/v Gerhard Zle TOR mek ATTORNEYS PROCESS FOR THE PRODUCTION OFSTRAIGHT- BEAD WELDED PIPE BACKGROUND OF THE INVENTION The presentinvention is related to a process for the manufacturing of straight-beadwelded pipes, preferably made of nonferrous metal, in which alongitudinally running metal band or strip is shaped into a split tube,the abutting edges are welded by means of an arc welder, and the metalpipe thus formed is subsequently treated further.

More particularly, the present invention is concerned with overcomingcertain problems inherently associated with such welded pipes. Thewelder creates a small zone of fusion in the immediate vicinity of thebutted seams, and this is of course the hottest zone. In a pipe (asopposed to welding flat plates, for example) the only direction for theheat induced by welding to travel is through the pipe wall in directionsaway from the weld. Thus, while the zone of fusion cools, solidifies andforms a fine grain structure, the matrix material adjoining the fusionzone has been subjected to a heat treatment, the intensity of whichinversely with distance from the fusion or weld zone. Thus, there may berecrystallization without fusion in an area very close to the fusionzone, but at a greater distance the effect of welding heat will be verysignificant grain growth. It will be appreciated that such grain growthin a thin or even thick walled pipe, and the non-homogeneous structureof the pipe in section, have very serious effects on the physical andmetallurgical properties of the pipe. Physical properties will beanisotropic, and metallurgical properties such as strain aging orresistance to stress corrosion fracture, changing at different rates atdifferent portions of the pipe, can lead to early failure.

One process is known for buttseam welding involving tempering of thewelding seam of aluminum or aluminum alloys, wherein the welding seam isremelted, in the absence of additional filler rods, and is thenrehardened. As a result, the impurities found in the welding seam shouldbe pushed in the direction of the external layer so that the nature ofthe junction or joint is changed at the median plane and the jointacquires and improved stability. Some decrease in grain size is at leastpossible here.

OBJECTS OF THE INVENTION A general object of the present invention is toprovide an improved method of producing straight-bead welded pipe, andapparatus for effecting same.

A further object of the present invention is to provide a method andapparatus for producing straightbead welded pipe with a homogeneous,equiaxed grain structure.

Another object of the present invention is to provide a method andapparatus for producing straight-bead welded pipe wherein themetallurgical effects of the welding on the pipe material aresubstantially eliminated.

Various other objects and advantages of the invention will become clearfrom the following description of embodiments, and the novel featureswill be particularly pointed out in connection with the appended claims.

THE DRAWINGS Reference will hereinafter be made to the accompanyingdrawings, wherein:

FIG. I is a simplified schematic diagram of an embodiment of theinvention;

.FIG. 2 is a more detailed schematic diagram of pipe deformationapparatus utilized in an embodiment of the invention;

FIG. 3 is a cross-section taken along line A-A of FIG. 2; and

FIG. 4 is a cross-section of a die utilized in a second embodiment ofthe invention.

DESCRIPTION OF EMBODIMENTS A straight-bead welded pipe is formed in theconventional manner, i.e. a strip of metal is formed into a tube or pipeby passing same through dies or forming rolls, and a continuous weldercloses the seam. Thereafter, the pipe is deformed, in accordance withthe invention, by both bending in the transverse plane and compressionin the longitudinal plane (both planes being with respect to the pipeaxis). By superimposing these two states of stress, the area around thewelding seam is cold-worked plastically to a high degree, forming alarge number of lattice distortions in the structure. These form nucleifor the new grains that are to be formed. The structure in the areaaround the welding seam becomes essentially finer in grain upon applyingthe process according to the invention than was possible by applyingpreviously known processes. I

The invention further concerns apparatus for the carrying out of theabove process. This device, according to the invention, may comprise apresser roll placed between two blocks which bend the metal pipe awayfrom and back to its continuous axis. The latter presser roll has a beadrunning around its periphery. With help of this device it is possible toproduce a compressive stress by means of the bead running in theperipheral direction in the area around the welding seam. It may beadvantageous in some cases to use a die instead of the presser roll,this die causing the metal pipe to be deflected and displaying aprojection which presses down on the welding seam. The width of thebeading should correspond at least to the width of the welding seam, sothat the entire area influenced structurally by the welding heat isunder the beading. The entire welding seam region is therefore shaped bythe presser roll so that coarsening of the grain is eliminated in themarginal zones of the welding seam. 1

In order to fully transfer the compressive stress of th presser roll orbead to the welding scam, the presser roll should be appropriatelyfurnished with a counter roll. Presser rolls and/or counter rollsaccording to the invention have a semicircular recess which runs in aperipheral direction and which is adjusted to the exter nal diameter ofthe metal pipe, thus preventing lateral sliding of the metal pipe.

With reference to the drawings, metal band 2 is removed from a storagedrum 1 and shaped by means of a molding tool (not shown) into a splittube 3, whose band edges are welded by means of an arc welding burner 4,under protective gas. According to the invention, metal pipe 5, forexample a copper pipe, is deformed in the area of welding seam 6 throughthe superimposing of two states of stress, i.e. by bending andcompressing it. Bending of the pipe takes place with the help of presserroll 7, which deflects metal pipe 5 from its continuous axis betweenguide blocks or rolls 8 and 9. Blocks 8 and 9 may also be dies. Thesecond stress state is forced on welding seam 6 through annular beading10 running in the peripheral direction with respect to presser roll 7.lnstead of presser roll 7, it is also possible to use a die 17 (see FIG.4). This should accordingly display a projection 18 corresponding tobeading 10. The width of beading 10 corresponds at least to the width ofwelding seam 6. In order to make it easier to transfer the compressivestress to welding seam 6 with the aid of beading 10, a counter roll 11is provided which is, obviously, not necessary when using a die. Presserroll 7 and counter roll 11 have semicircular recesses 19, 20corresponding to the external diameter of metal pipe 6, which serve forthe transport of metal pipe 5. After deformation takes place, metal pipe5 runs through a continuous annealing furnace 13, which can be heatedfrom outside. However, metal pipe 5 can also be annealed in this furnacebetween two current-conveying rolls by means ofjoulean heat.

After annealing, the dent 14 pressed into pipe 5 via beading 10 ispressed out again by means of a mandrel (not shown), which is known initself. it is also possible to simultaneously reduce the externaldiameter of metal pipe 5 and reduce wall thickness by means of anextruding device 15. Following this cold-working process, metal pipe 5is annealed again in another annealing furnace 16, which can be builtlike annealing furnace 13, so that the welding seam is tempered onceagain. Lastly, the prepared metal pipe 5 is wound up by well knownmethods on hoops or drums in a lengthwise direction.

Various changes in the details, materials, steps, and arrangements ofparts, which have been herein described and illustrated in order toexplain the nature of the invention, may be made by those skilled in theart within the principle and scope of the invention as defined in theappended claims. One example of a variation is to repeat thebending-compression deformation, followed by an additional anneal. Itwill also be appreciated that the invention is equally adapted for usewith discrete lengths of pipe, though it will generally be employed withcontinuous production equipment.

What Is Claimed Is:

1. Process for the homogenization of straight-beam welded pipecomprising:

plastically deforming said pipe in the region of said weld by bothbending and compression; 5 said bending being away from and back to theiongitudinal axis of said pipe; said compression being carried out bydeforming a region including the weld zone inwardly toward thelongitudinal axis; and I annealing said pipe to produce a homogeneousgrain structure.

2. The process as claimed in claim 1, wherein said bending is carriedout by passing said pipe between guide means coaxial with the axis ofsaid pipe and a roll 15 intermediate said guide means, the periphery ofsaid roll being spaced from the axis of said pipe, said pipe beingrbentin passing over said roll 3. he process as claimed 1n claim 2, andadditionally comprising compressing the weld zone of said pipe towardsaid axis as it passes over said roll.

4. The process as claimed in claim 3, wherein said compression iseffected with a peripheral bead on said roll adapted to engage said weldzone, and additionally comprising forcing said pipe against said beadwith a counter roll engaging the side of said pipe opposite said weldzone.

5. The process as claimed in claim 1, where said bending and compressionare carried out by passing said pipe through a die located intermediatea pair of guide means coaxial with the longitudinal axis of said pipe,the axis of said die being spaced from the axis of said pipe.

6. The process as claimed in claim 5, wherein said compression isprovided by a longitudinal bead within said die at least as wide as theweld zone and located so as to compress said weld zone inwardly.

7. In a process for the production of straight-beam welded pipe whereina strip of metal is formed into a tube with butting edges, said edgesare welded and the pipe thus formed is further treated to produce afinal product, the improvements comprising subjecting the zone of saidwelding to plastic deformation by both bending and compression, saidbending being away from and back to the longitudinal axis of said pipe;said compression being carried out by deforming a region including theweld zone inwardly toward the longitudinal axis; and annealing thedeformed pipe to produce a homogeneous grain structure.

1. Process for the homogenization of straight-beam welded pipecomprising: plastically deforming said pipe in the region of said weldby both bending and compression; said bending being away from and backto the longitudinal axis of said pipe; said compression being carriedout by deforming a region including the weld zone inwardly toward thelongitudinal axis; and annealing said pipe to produce a homogeneousgrain structure.
 2. The process as claimed in claim 1, wherein saidbending is carried out by passing said pipe between guide means coaxialwith the axis of said pipe and a roll intermediate said guide means, theperiphery of said roll being spaced from the axis of said pipe, saidpipe being bent in passing over said roll.
 3. The process as claimed inclaim 2, and additionally comprising compressing the weld zone of saidpipe toward said axis as it passes over said roll.
 4. The process asclaimed in claim 3, wherein said compression is effected with aperipheral bead on said roll adapted to engage said weld zone, andadditionally comprising forcing said pipe against said bead with acounter roll engaging the side of said pipe opposite said weld zone. 5.The process as claimed in claim 1, where said bending and compressionare carried out by passing said pipe through a die located intermediatea pair of guide means coaxial with the longitudinal axis of said pipe,the axis of said die being spaced from the axis of said pipe.
 6. Theprocess as claimed in claim 5, wherein said compression is provided by alongitudinal bead within said die at least as wide as the weld zone andlocated so as to compress said weld zone inwardly.
 7. In a process forthe production of straight-beam welded pipe wherein a strip of metal isformed into a tube with butting edges, said edges are welded and thepipe thus formed is further treated to produce a final product, theimprovements comprising subjecting the zone of said weldiNg to plasticdeformation by both bending and compression, said bending being awayfrom and back to the longitudinal axis of said pipe; said compressionbeing carried out by deforming a region including the weld zone inwardlytoward the longitudinal axis; and annealing the deformed pipe to producea homogeneous grain structure.